The present invention relates generally to improvements in electronic shelf label (ESL) systems used in transaction establishments. More specifically, the present invention relates to advantageous aspects of a wireless ESL communication system.
ESL systems typically include a plurality of ESLs for each merchandise item in a store. ESLs display the price of corresponding merchandise items on store shelves and are typically attached to a rail along the leading edge of the shelves. A store may contain thousands of ESLs to display the prices of the merchandise items. The ESLs are coupled to a central server where information about the ESLs is typically maintained in an ESL data file which contains ESL identification information and ESL merchandise item information. Price information displayed by the ESLs is obtained from a price look-up (PLU) data file. The central server sends messages, including price change messages, to the ESLs through a communication base station (CBS) which may be mounted in the ceiling of the retail establishment.
The communications link from the CBS to an ESL, known as the xe2x80x9cdownlinkxe2x80x9d, uses infrared (IR) or radio frequency (RF) technology. To ensure that a message transmitted to the ESL was properly received, the ESL transmits a positive acknowledgement over an xe2x80x9cuplinkxe2x80x9d communication path to the CBS, which in turn relays the acknowledgment to the central server. The downlink communications path is separate from and may employ different technology than the uplink communication path, since the uplink path transmits much less data than the downlink path. For example, the ESL may transmit an acknowledgement which consists of a single status byte.
Not only is it important for the communication links to be reliable, but for ESL systems to be cost effective, ESLs must be inexpensive and the cost of the infrastructure, such as the CBS, kept to a minimum. Since the downlink is transmitted from the CBS which may be operated by an external power source, providing transmission power for the downlink is not usually a concern. However, the uplink signal is originated by the ESL, which is typically powered by a battery. Since battery life of the ESL is an important design consideration, utilizing an active uplink which actively transmits an RF or IR signal may consume excessive power and reduce battery life.
Thus, it would be desirable to provide a reliable uplink communication path for an ESL system which consumes minimal battery power while providing a large communication range.
The present invention advantageously provides methods and apparatus for an ESL system which uses the ESL""s liquid crystal display (LCD) to transmit information to a relay unit, or CBS, by reflecting infrared (IR) or visible light to the relay unit. In a first embodiment, a plurality of IR light sources flood the area where the ESL is located. To transmit a message to the relay unit, the ESL reflectively modulates the IR light by blinking, or turning on and off, at least one segment of the LCD display. The relay unit then receives and interprets the modulated reflected IR light. In a second embodiment, the relay unit does not generate IR light. Instead, the ESL reflectively modulates the visible light present in the retail establishment to transmit a message to the relay unit. The relay unit may use one or more cameras to receive this reflectively modulated visible light.
A more complete understanding of the present invention, as well as further features and advantages of the invention, will be apparent from the following detailed description and the accompanying drawings.